This invention relates to a calibration device capable of generating a predetermined fluorescent emission, and then directing that emission towards a fluorescence photometer. By comparing the fluorescent emission read by the photometer with the actual emission from the calibration device, a determination can be made as to whether the photometer is accurately reading fluorescent emissions.
Fluorescence photometers are utilized in the evaluation of biological fluid samples. As one example, a body fluid sample, such as blood, may be placed with a culture medium in a test tube, along with a fluorescent chemical sensor responsive to biological activity. Known methods are utilized for directing an excitation radiation into the sample, and then reading the fluorescent emission from that sample. By comparing the emission to expected values, a determination can be made of whether bacterial activity is ongoing in the sample being evaluated. For purposes of this application, a "Fluorescence photometer" would also include any instrumentation incorporating a fluorescence measuring subsystem.
One aspect of such photometers is that they must be properly calibrated to be effective. If the photometer is not accurately reading the fluorescent emission, then the readings from that photometer will not provide accurate evaluations of the sample being tested. Thus, initial and periodic calibration must be performed on such photometers.
In the prior art, passive fluorescent standards are utilized to test the accuracy of fluorescence photometers. Such fluorescent standards may be a standard object, including a solid compound having known fluorescent properties. Other types of passive fluorescence standards are provided by liquid chemical compounds meant to approximate particular fluorescent characteristics of biological or chemical samples to be tested. These liquid or "fresh chemical" standards are subject to formulation problems and lot-to-lot variations.
For either type of passive standard, problems exist due to different responses by the standard to temperature, irreversible degradation with heat or time, and bleaching with repeated exposure to light (as could be caused by the excitation radiation directed from the fluorescent photometer). When the standard has characteristics that are different than expected, from its specified or tabulated values, incorrect readings will result at the photometer. An operator may then determine that a properly calibrated photometer requires adjustment or repair when, in fact, it is the standard which caused the inaccurate result.
Moreover, the evaluation of the fluorescent emission from such standards is necessarily compared to what is believed to be the excitation radiation generated by the fluorescence photometer under test. If the excitation radiation is out of tolerance (such as when it is the excitation portion of the photometer which requires adjustment), typical passive fluorescent standards may result in an indication that a properly calibrated photometer is improperly calibrated. That is, if the excitation radiation is different from specification, then the fluorescent radiation emitted by the standard will also be different than expected. The fluorescent photometer may accurately read the actual fluorescent emission, but could be identified as being "out of calibration," when in fact the excitation radiation is actually out of tolerance.
These various drawbacks with the use of fluorescent standards create difficulties in calibrating, repairing, manufacturing, and testing photometers.